Method and mobile communication network for providing multicast and/or broadcasting services

ABSTRACT

Disclosed are methods and systems for providing multicast and/or broadcast services in a mobile communication network. In particular, the disclosed methods and systems optimize resource utilization and signaling in packet-based networks.

CLAIM FOR PRIORITY RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.10/492,692 filed Oct. 20, 2004 now U.S. Pat. No. 7,580,718, which is anational stage application of International Application No.PCT/DE01/04037, filed in the German language on Oct. 19, 2001. Thecontents of these applications are incorporated herein in their entiretyby this reference.

FIELD OF THE INVENTION

The present invention relates to a method and a mobile communicationsnetwork for provision of multicast and/or broadcast services.

BACKGROUND OF THE INVENTION

Mobile communications networks may be connected with the aid of GPRS(General Packet Radio System) or UMTS (Universal MobileTelecommunications System) as packet-switching systems to furtherstandard data networks which are based on the packet-switchingprinciple, so-called packet data networks, such as the Internet. Data isin this case transported by a packet data network, for example theInternet, via a GPRS or UMTS network to a mobile communication unit (MS)using a number of standardized protocols, such as IP (InternetProtocol). The general configuration of a GPRS mobile radio networkincluding in particular serving GPRS support nodes (SGSN) and gatewayGPRS support nodes (GGSN) is known from the specialist journal“Funkschau” [Radio Show], 20/99, “IP im Mobilfunk” [IP in mobile radio].Data coming from a public packet-switching network is transmitted bymeans of point-to-point connections or services (PtP services) via aGGSN to an SGSN, and from there to a mobile communication unit. In asystem such as this, an SGSN has monitoring functions (relating, forexample, to user mobility, user authorization, transport servicemonitoring, service access monitoring) and packet transport functions(such as the conversion of data between the transport tunnels to theGGSN or to the radio network). A GGSN controls the connection between aGPRS network and a packet-data-oriented external landline network, forexample the Internet. A GGSN furthermore converts data packets betweenan external packet-switching landline network and a transport tunnelbetween a GGSN and SGSN.

UMTS and GSM/GPRS provide an IP multicast service which allows mobileusers to receive multicast data. This multicast service is based onpoint-to-point connections (PtP) between a mobile communication unit(MS) and the GGSN. The multicast data comes, for example, from themobile communications network or from a packet-oriented externallandline network, for example the Internet, by means of a multicastserver, for example. This multicast service does not, however, ensureefficient use of the resources available. A separate connection as faras the multicast function of the GGSN for the respective MC-IP addressis set up, and the multicast service is thus produced, viapoint-to-point connections for each mobile communication unit (MS) whichwishes to use a specific multicast service.

SUMMARY OF THE INVENTION

The invention accordingly optimizes the resource utilization and thesignaling for the provision of multicast and/or broadcast services inpacket-based networks.

According to the invention, this object is achieved by the methods andby the mobile communications network (described therein).

In one embodiment a method for provision of multicast (MC) and/orbroadcast services for a mobile communications network which includes aradio network and a core network is provided. The method having at leastthe following steps:

-   a. transmission of multicast and/or broadcast data for a multicast    service (MC) which is activated by at least one mobile communication    unit, and/or for a configured broadcast service from an MC source to    the at least one mobile communication unit via at least one    communication node, which is arranged in the core network, using a    service-specific context (MC context) which is stored in the    communication node,-   b. control and monitoring of the transmission of the multicast data    to the at least one mobile communication unit through the at least    one communication node, which is arranged in the core network, using    a context which is stored in the communication node and is specific    for precisely that at least one mobile communication unit with    reference to the activated multicast service, and/or-   c. broadcasting of the broadcast data for the configured broadcast    service in a defined region.

The invention reduces the number of nodes required and the resourcesrequired for packet transmission of multicast and/or broadcast data. Inthis case, the method and the mobile communications network can beintegrated well in the known UMTS and GSM/GPRS architecture. Thecommunication node in the core network is generally an SGSN for a GSM orUMTS mobile communications network. The MC and/or broadcast serviceswhich can be provided according to the invention are in this caselargely downwards-compatible to UMTS and GSM/GPRS point-to-point (PtP)IP services. This considerably simplifies the implementation of thecorresponding services in the known network systems, and assists thedownwards compatibility. The MC source may in this case be an MC serverin an external network, or an MC server from the mobile communicationsnetwork.

In one preferred embodiment of the method according to the invention,the context which is specific for the at least one mobile communicationunit is additionally stored in the at least one mobile communicationunit.

The form of a specific PDP context (MC PDP context) is preferably chosenfor the context which is specific for the at least one mobilecommunication unit and is stored in the communication node. Thiscontext, which is specific for the at least one mobile communicationunit with respect to the activated multicast service and is stored inthe communication node that is arranged in the core network in this casepreferably includes all of the parameters which are specific for themulticast service that is activated by the mobile communication unit.This includes, for example, a so-called QoS profile, or else is referredto as a service quality profile. This profile indicates the relevantquality parameter, such as the bit rate/bandwidth, packet transmissiontime, priorities, etc. The QoS profile indicates to the communicationnode that is arranged in the core network the transmission capabilitiesof the mobile communication unit. Furthermore, the MC PDP contextcontains the access point name (APN) for each multicast service which isactivated by the mobile communication unit. This indicates the homenetwork or the administrative domain to which the MC IP address of therelevant multicast service belongs. The context furthermore contains theMC IP address of the relevant MC service.

Each multicast (MC) and/or broadcast service is preferably allocated aservice-specific MC-TMSI, which is based on the fundamentalconfiguration of the known TMSI. This allows multicast and broadcastnotification using existing procedures. This MC-TMSI is preferablylikewise contained in the MC PDP context of the mobile communicationunits which make use of the service.

In one preferred embodiment of the method according to the invention,the multicast and/or broadcast data is encrypted on a service-specificbasis by means of a service-specific encryption code for thetransmission from the communication node to the mobile communicationunit. This encryption code is likewise recorded in the MC PDP contextfor the at least one mobile communication unit of the mobilecommunication units which make use of the service, and in theservice-specific context (MC context) which is stored in thecommunication node. The data is either encrypted directly by the MCsource, or else the communication node, that is to say in general theSGSN, carries out the encryption task. In a situation where thecommunication node, that is to say the SGSN, carries out the encryptionprocess, then it sends the encryption code to a mobile communicationunit when the mobile communication unit activates the relevant MCservice and when a general update of the MC service is carried out. Theencryption code is in this case preferably transferred via individualPtP signaling channels, which are already encrypted by existingencryption mechanisms. The encryption code is preferably changed atperiodic intervals. Since it is impossible to ensure that all of themobile communication units which have activated the relevant MC servicereceive the new changed encryption code at the same time, the MC datafor the relevant MC service is sent a number of times in parallel, butin each case encrypted using a different encryption code. The encryptionprocess is preferably carried out on the basis of IPSec (InternetProtocol Security).

In one preferred embodiment of the method according to the invention,the at least one communication node which is arranged in the corenetwork, that is to say in general the SGSN, carries out registrationand signaling functions with respect to an activated multicast service.

In one preferred embodiment of the method according to the invention,the at least one communication node which is arranged in the corenetwork carries out authentication and authorization functions withrespect to an activated multicast service using means which are definedfor point-to-point services (PtP services). In this case, the existingstructure of authorization data can be used by PtP services whenspecific multicast services require dedicated authorizations. An MCservice is activated by a mobile communication unit by means ofindividual signaling between the communication node and the mobilecommunication unit. In this case, according to the invention, extendedPtP service signaling is preferably used, that is to say the multicastservice is activated by an additional element, the extended NSAPI(Network Layer Service Access Point Identifier), in the signalingbetween the at least one mobile communication unit and the communicationnode. An optional signaling element, specifically an extended or MCNSAPI (Network Layer Service Access Point Identifier) is introduced inthis case. This signaling element allows a greater number of PDPcontexts which are set up in parallel and are limited by the value rangeof the NSAPI. This can be important when one MS is using two or more MCservice s in parallel, since an individual NSAPI is used at least forsignaling of each MC service in a mobile communication unit.

The individual signaling of an MC service by a mobile communication unitmakes it possible for the communication node to authenticate therelevant mobile communication unit by means which are already definedfor PtP services. Furthermore, by comparison with the correspondingauthorization data for the mobile communication unit in the HLR (HomeLocation Register), the communication node can check whether the mobilecommunication unit is authorized to activate and to use the relevant MCservice. The authorization data for an MC service in the HLR has thesame structure as the corresponding authorization data for a PtPservice. Furthermore, it is preferably possible to use the MC servicewith normal conventional GPRS authorization (entered in the HLR) aswell. The type of authorization that is demanded for activation of aspecific MC service can preferably be derived from the MC-IP addressand/or from the APN of the relevant MC service. The MC-IP address and/orthe APN which are/is required for authorization are/is stored in thecommunication node. The use of known CAMEL functionalities offers afurther option for checking whether or not an MC service can beactivated.

A mobile communication unit which wishes to receive MC data for an MCservice preferably activates this service first, as already explained,by signaling which contains the extended or MC NSAPI. The activation ofthe first MC service for this mobile communication unit results in afirst MC PDP context being created, which is stored in the communicationnode and in the mobile communication unit. As already explained, thiscontext preferably contains all of the parameters which are specific forthe relevant MC service and for the mobile communication unit. Thecontext is linked to the mobility management (MM) for the mobilecommunication unit in the same way as PDP context which is used for aPtP service. For each further MC service which is activated and used bythe mobile communication unit in the subsequent time, only data which isrelevant for this further MC service is additionally included in thealready existing MC PDP context in the MS and in the communication nodewhich is arranged in the core network. When a specific MC service isactivated for the first time in the responsibility area of thecommunication node, then an MC context is additionally created in thecommunication node, preferably containing all of the parameters whichare specific for this MC service. This context preferably has a list ofthose mobile communication units which have activated this multicastservice.

This means that it is possible to supply multicast and/or broadcast datafor at least one multicast and/or broadcast service to two or morecommunication units (MS) at the same time by means of one and the samecontext (MC context), which is specific for the at least one multicastand/or broadcast service.

The at least one communication node which is arranged in the corenetwork then preferably controls the setting-up and clearing oftransmission channels in the multicast service. The communication nodeinitiates, inter alia and for example, the IP multicast connection onthe IP backbone for the relevant MC IP address.

The “configuration options” parameter, which is known from PtP services,allows the user and the mobile communication unit to provide even moreinformation, such as the tariff for the MC service.

The described procedure in the case of the provision of MC services canalso be used, with minor discrepancies, for the provision of broadcastservices. In order to provide broadcast services, a so-called MC-TMSI isreserved or allocated on a service-specific basis for each broadcastservice, and its configuration is essentially based on a known TMSI.Each mobile communication unit which wishes to use a specific broadcastservice has to monitor the corresponding signaling channels in order toreceive notifications with the MC-TMSI that is associated with thecorresponding broadcast service. These MC-TMSIs may, for example, beconfigured in the mobile communication unit. Furthermore, an MC contextwhich preferably includes all the service-specific parameters is createdand stored on each communication node which provides the broadcastservice. This MC context has, for example, the MC-TMSI that isassociated with the relevant broadcast service, its IP-MC address, aservice-specific QoS profile for the transmission channels between thecommunication node and the mobile communication units which receive thedata and, finally, the region in which the broadcast service isprovided, which may correspond, for example, to a list of radio cells.Only radio resources in those cells in which there are mobilecommunication units which wish to use the relevant broadcast service arepreferably used for the provision of broadcast services.

In network structures which use Iu flexibility, it is possible for twoor more communication nodes to control the same region. In this case, MCdata for the same MC service may arrive at a region having two or morecommunication nodes at the same time. These data transmissions arecoordinated by the radio network. The radio network uses the MC-TMSIthat is associated with the relevant MC service to detect thatnotifications coming from different communication nodes originate fromone and the same MC service. All the communication nodes in this casepreferably use the same MC-TMSI for one specific MC service. The radionetwork determines the overall region in which mobile communicationunits which are making use of the relevant MC service are located, onthe basis of the regions which are indicated in the notifications comingfrom the various communication nodes. It is also advantageous likewiseto always select the same for a specific MC service as the encryptioncode in the various communication nodes. Otherwise, coordination isimpossible. The encryption codes, like the MC data as well, would thenbe handled independently of one another and thus in parallel, whichwould be inefficient. In contrast to MC services, a specific broadcastservice is only ever configured in one of the two or more communicationnodes which control the same region. This means that there is nopossibility of two or more communication nodes sending broadcast datafor the same broadcast service to the same region at the same time.

As already mentioned, the method according to the invention is verylargely downwards compatible with UMTS and GSM/GPRS point-to-point (PtP)IP services. In the situation where a communication node does notsupport MC services corresponding to the method according to theinvention then, instead of this, it automatically activates a PtPservice. As already mentioned, the signaling for an MC service isvirtually identical to the signaling for a PtP service. A communicationnode which does not support the MC services described above in this casesimply ignores the optional signaling element MC NSAPI, andautomatically activates a PtP service. A communication node which doessupport the provision of the described MC services can also choose, whenMC signaling arrives, whether it will activate a PtP service or an MCservice. If, for example, the number of mobile communication units whichare using a specific MC service is small, then it is often moreefficient to activate a PtP service rather than an MC service.

If MC and/or broadcast data now have to be transferred, thentransmission channels are set up between the communication node and thecorresponding mobile communication units MC and/or broadcast. Theactivation of the transmission channels between the communication nodeand the mobile communication units starts as soon as the communicationnode has received MC and/or broadcast data from the relevant MC IPaddress. The communication node then sends a notification to the radionetwork stating the MC-TMSI of the relevant service and the region inwhich mobile communication units which are using the relevant serviceare located. In the case of a broadcast service, the communication nodeindicates in the notification which region is configured in the MCcontext for the relevant broadcast service.

After receiving a notification such as this, the radio network requeststhe communication node to set up one or more transmission channelsbetween the communication node and the radio network. The radio networkmay, for example, in this case arrange different transmission channelsfor different regions. The transmission channels between thecommunication node and the radio network are set up using a QoScharacteristic which corresponds to the QoS profile for the relevant MCor broadcast service, and is indicated in the associated MC context.This QoS profile at the same time also indicates the requirements whichhave been placed on the radio transmission channels, that is to say onthe transmission channels to be set up between the radio network and themobile communication units.

The radio network then sends a notification to all of the mobilecommunication units which are located in the region indicated by thecommunication node, stating the MC-TMSI for the relevant service. Thisnotification may be carried out, for example, by the known “paging”mechanism. The “paging” is in this case preferably repeated at periodicintervals until the transmission channels have been set up between theradio network and the mobile communication units. After receiving thenotification, the relevant mobile communication units wait for a certainamount of time before they themselves request that radio transmissionchannels be set up. If a mobile communication unit does not receive anyindication of the radio transmission channels that have been set upwithin this time, then it requests that a radio transmission channel beactivated by the radio network.

The radio network preferably sets up radio transmission channels for MCservices and broadcast services only in those regions where it receivesrequests from mobile communication units. The radio network sends the MCand/or broadcast data received from the communication node to the mobilecommunication units via the corresponding radio transmission channels.

As soon as no more data is received by the communication node, it canadvantageously clear the transmission channels between it and the radionetwork. This means that the radio network likewise clears thecorresponding radio transmission channels which are involved in the datatransmission.

The method according to the invention furthermore also ensures themobility of mobile communication units when they are using MC services.If a mobile communication unit which is activated one or more MCservices moves from the responsibility region of one communication nodeto the responsibility region of another communication node, then thecontinued provision of the one or more activated MC services is ensuredin that the MC PDP context which is stored for the relevant mobilecommunication unit is transferred from the old communication node to thenew communication node together with the other contexts which arespecific for the mobile communication unit. The new communication nodehandles the MC PDP context in the same way as if the one or more MCservices which are being used by that mobile communication unit havebeen reactivated by the mobile communication unit. If, by way ofexample, no MC service has yet been activated in the new communicationnode, then a new MC context, which is specific for that MC service, isset up. If, on the other hand, the MC service has already been providedfor other mobile communication units by the new communication node, thenan MC context already exists, in which the newly arriving communicationunit is also included. The encryption code may be changed if necessary,and, if appropriate, this is signaled to the relevant mobilecommunication unit from the new communication node. Furthermore, it ispossible to change the MC-TMSI which is associated with the MC service,and this is then likewise signaled to the relevant mobile communicationunit. In a situation where the QoS capabilities of the mobilecommunication unit are not adequate to use the MC service or servicesvia the new communication node, or where the location of the mobilecommunication unit is not permissible for the MC service or services,then the MC service or services for the relevant mobile communicationunit is or are deactivated by the new communication node.

The present invention can also provide a mobile communications networkwhich is suitable for carrying out the method according to theinvention.

In one embodiment, a mobile communications network for provision ofmulticast and/or broadcast services is described. The mobilecommunications network includes

-   a. an MC source,-   b. a core network,-   c. a radio network with a radio interface for wire-free transmission    of multicast and/or broadcast data to at least one mobile    communication unit (MS),-   d. a communication node which is arranged in the core network and in    which in each case at least one service-specific context (MC    context) is provided for controlling the transmission of the    multicast and/or broadcast data for an activated multicast and/or    broadcast service, which service-specific context (MC context)    comprises all the service-specific parameters and, additionally in    the case of a multicast service, in each case one context, which is    specific for the corresponding mobile communication unit with    respect to the activated multicast service, for all of the mobile    communication units which have activated the multicast service, and-   e. at least one communication node which is arranged in the radio    network and in which notifications as well as MC and/or broadcast    radio transmission channels are provided for controlling the    transmission of the multicast and/or broadcast data for an activated    multicast and/or a configured broadcast service.

DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will be described withreference to the following figures, in which:

FIG. 1 shows, in the form of a block diagram, the use of methodsaccording to the invention for the activation of an IP MC service,

FIG. 2 shows, in the form of a block diagram, the use of methodsaccording to the invention which ensure mobility between thecommunication nodes which are arranged in the core network, and

FIG. 3 shows, in the form of a block diagram, the use of methodsaccording to the invention for the transmission of MC and/or broadcastdata.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the activation of an MC service, in the form of a blockdiagram. The user or an application which is provided in a correspondingmanner on a mobile communication unit MS initiates the use of an MCservice. In a step 1 which is similar to that for activation of a PtPservice, the mobile communication unit MS sends an activation request, aso-called activate PDP context request, to an associated communicationnode in the core network, that is to say in general to a responsibleSGSN. This activate PDP context request comprises the indication of theaccess point name (APN), the PDP address, the QoS profile, the extendedor MC NSAPI and further parameters which are defined for a PtP service.The APN indicates the home network or the administrative domain to whichthe MC IP address belongs. This can be used to derive an appropriateGGSN, for example if a PtP service is being activated rather than an MCservice. The PDP address corresponds to the IP MC address to which theMS is to set up a connection. The QoS profile indicates the QoScapabilities of the MS. The extended or MC NSAPI corresponds to theindex of the MC service within the MC PDP context.

In a similar way to that for activation of a PtP service, securitymeasures (security functions) may be implemented in a step 2, such asthe authentication of the MS.

The communication node, that is to say the SGSN, checks whether aspecific authorization is required in addition to the general GPRSauthorization for the requested MC service, and if the answer is yes,whether the user has the corresponding authorization. The relevant MCservice may possibly demand specific QoS capabilities. If the MS cannotsatisfy these QoS requirements, then the SGSN rejects the activate PDPcontext request. Otherwise, the SGSN creates an MC context for therelevant IP MC address, and transfers the QoS capabilities of the MS tothe QoS profile of the MC context, if no MC context already exists forthe relevant IP MC address in the SGSN. However, if an MC contextalready exists for the relevant IP MC address and the MC service doesnot demand any particular QoS requirements, the SGSN compares the MC QoScapabilities with the QoS profile of the MC context. Each individualparameter in the QoS profile is in this case set to the respectiveminimum of the corresponding QoS parameters for the MC context or forthe MS QoS capabilities. In a step 3, which is referred to as “Join IPMulticast”, the SGSN enters the IP MC service for the corresponding MCIP address on the IP backbone, if it is the first MS to activate this MCservice. Otherwise, SGSN has already entered IP MC service for thecorresponding MC IP address on the IP backbone.

In a step 4, the SGSN sends an acceptance message, a so-called activatePDP context accept, precisely in the same way as a PtP service, to theMS. This acceptance message contains the MC-TMSI for the requested MCservice, the MC encryption code, the extended/MC NSAPI and furtherdefined parameters for a PtP service. The MC-TMSI is specific for one MCservice and is used to inform the MS of an MC data transfer(notification) All MS which have activated a specific MC service observethe signaling channels for notifications with the MC-TMSI of therelevant MC service.

FIG. 2 uses a block diagram to show the mobility between twocommunication nodes and between two SGSNs for the provision of MCservices.

An MS is moving from the responsibility area of a first, old SGSN O tothe responsibility area of a second, new SGSN N. In the process, the MSsends a request in a step 1 to the new SGSN N, in order to update thelocation region (routing area), a so-called “Routing Area UpdateRequest”. The new SGSN N sends a request in a step 2 to the old SGSN Oand requests the contexts relating to the MS, a so-called contextrequest. In a step 3 the old SGSN O then sends all of the contexts whichare stored for this MS in a corresponding response message, theso-called context response, to the new SGSN N. Once again, securitymeasures (security functions) are carried out by the new SGSN N in astep 4. In a step 5, the new SGSN N sends a recognition message, aso-called context acknowledge message, to the old SGSN O, in order toindicate that it has taken over control of the MS. All the measures forprovision of the authorization and security data in the new SGSN N andfor registration of the new SGSN N in the HLR are carried out. The newSGSN N then evaluates the presence of the MS, that is to say it checkswhether the MS has any authorization at all to receive data via the newSGSN N. Furthermore, the new SGSN N checks each individual MS servicewhich is indicated in the MC PDP context of the relevant MS. If thisincludes an MC service for which no MC context is yet stored in the newSGSN N, then the new SGSN N creates an appropriate MC context and entersthe corresponding IP MC service on the IP backbone in step 6. If MCcontexts for MC services which are listed in the MC PDP contexts for MSexist in the new SGSN N, then the new SGSN N compares the respective QoSprofiles of its MC contexts with the QoS profile of the MS and, ifpossible, appropriately adapts the parameters. If the new SGSN N uses adifferent MC-TMSI for a specific MC service than the old SGSN O, or usesa different encryption code for the MC data for a specific MC service,then the new parameters for the MS are sent in a step 7. The sameMC-TMSI is advantageously used for the same IP MC address in all theSGSNs. The new SGSN O can now receive corresponding MC data in a step 8.A handover or a relocation can likewise lead to a change to the SGSN. Inthis case, in contrast to the SGSN change described above, PtP servicesare also activated by the MS in parallel with the MC service. In thissituation, handover/relocation signaling takes place, inter alia,between the two SGSNs. In this case, the old SGSN O sends the PDPcontexts of the MS to the new SGSN N, in order that the new SGSN N cancheck whether it can continue these services and has the necessaryresources. In this way, the new SGSN N also receives the MC PDP contextfor the MS. If the new SGSN N has accepted the handover or therelocation, it evaluates the MC PDP context and carries out thenecessary actions with respect to MC services.

One possible MC data transfer is illustrated in FIG. 3 on the basis of ablock diagram. An MC source (for example an MC server) with a specificMC IP address, which offers a specific MC service, sends MC data in astep 1, which is received by at least one SGSN with an MC context thatis associated with the MC IP address. In a step 2, the SGSN then sendsat least one notification to at least one radio network. Thisnotification contains an MC-TMSI which is associated with the relevantMC service, and all the location regions in which mobile communicationunits MSS which have activated the relevant MC service are located. In astep 3, the radio network responds by sending one or more requests,so-called MC service requests, to the SGSN which initiate the setting upof MC transmission channels. The radio network may possibly require twoor more MC transmission channels, for example for different locationregions. In a step 4, the SGSN then sends an MC transmission channelrequest, a so-called MC Bearer Request Message, to the radio network,for each request. These requests contain the QoS parameters which the MCtransmission channels between the SGSN and the MS must have. For eachrequest from the SGSN, the radio network sends a response in a step 5, aso-called MC Bearer Response, to the SGSN, by which means an MCtransmission channel is in each case set up between the radio networkand the SGSN. The radio network sends notifications, indicating theMC-TMSI, to all the cells in the location regions which arepredetermined by the SGSN and in which MS are located which haveactivated the relevant MC service. Those MS which have activated therelevant MC service and have received a notification wait for a certaintime for an MC radio indication message (MC radio assignment), whichdescribes the MC radio transmission channel via which the MC data willbe transferred. If an MS does not receive any such MC radio indicationmessage, then, in a step 7, the MS sends a request, a so-called MC radiorequest, to the radio network, in order to initiate the setting up of anMC radio transmission channel.

The radio network sets up one or more MC radio transmission channelsand, in a step 8, sends one or more corresponding MC radio indicationmessages to all the relevant cells. Once the MC transmission channel orchannels has or have been completely set up between the SGSN and theradio network, the SGSN starts, in a step 9, to transmit to the radionetwork the MC data received from the relevant IP MC address. In a step10, the radio network then sends this MC data to the corresponding radiotransmission channel/channels. If the SGSN does not receive any more MCdata, then it releases the MC transmission channel or channels to theradio network, and these transmission channels are cleared in a step 11(MC Bearer Release). This means that, in a step 12, the radio networklikewise clears the corresponding radio transmission channels (MC RadioRelease). This is reported to the relevant MS.

1. A method for changing the path for receiving a multicast service by amobile communication device from a first communication node to a secondcommunication node, the method comprising the steps of: transmitting aRouting Area Update Request by the mobile communication device to thesecond communication node; transmitting a Context Request by the secondcommunication node to the first communication node; transmitting aContext Response by the first communication node to the secondcommunication node, said Context Response comprising the context forsaid multicast service; transmitting a Context Acknowledgement by thesecond communication node to the first communication node to indicatethat the second communication node has control over the mobilecommunication device; checking, by the second communication node,whether it has stored a multicast Packet Data Protocol (PDP) (MC-PDP)context for said multicast service that is indicated in the ContextResponse; and if not, creating by the second communication node a newMC-PDP context for said multicast service and entering said multicastservice on a backbone network.
 2. The method according to claim 1,comprising the further steps of: transmitting an Update Location by thesecond communication node to a Home Location register (HLR);transmitting a Cancel Location by the HLR to the first communicationnode; transmitting a Cancel Location Ack by the first communication nodeto the HLR; transmitting an Insert Subscriber Data by the HLR to thesecond communication node; transmitting an Insert Subscriber Data Ack bythe second communication node to the HLR; transmitting an UpdateLocation Ack by the HLR to the second communication node.
 3. The methodaccording to claim 2, comprising the further steps of: transmitting aRouting Area Update Accept by the second communication node to themobile communication device; transmitting a Routing Area Update Completeby the mobile communication device to the second communication node. 4.The method according to claim 1, comprising the further steps of:transmitting a Routing Area Update Accept by the second communicationnode to the mobile communication device; transmitting a Routing AreaUpdate Complete by the mobile communication device to the secondcommunication node.
 5. The method according to claim 1, wherein thesecurity functions use encryption.
 6. The method according to claim 1,wherein the first and second communication nodes are arranged within amobile communication network.
 7. The method according to claim 6,wherein the mobile communication network uses GPRS or UMTS.
 8. Acommunication node, comprising: means for receiving a Routing AreaUpdate Request by a mobile communication device, said request comprisingan indication of another communication node presenting serving themobile communication device; means for transmitting a Context Request tothe other communication node; means for receiving a Context Responsefrom the other communication node; means for transmitting a ContextAcknowledgement to the other communication node to indicate that thecommunication node has control over the mobile communication device;means for checking whether the communication node has stored a multicastPacket Data Protocol (PDP) (MC-PDP) context for a multicast service thatis indicated in the Context Response; and means for creating a newMC-PDP context for said multicast service and entering said multicastservice on a backbone network if the communication node has not stored athe MC-PDP context for the multicast service.
 9. The communication nodesaccording to claim 8, further comprising: means for transmitting anUpdate Location to a Home Location register (HLR); means for receivingan Insert Subscriber Data from the HLR; means for transmitting an InsertSubscriber Data Ack to the HLR; means for receiving an Update LocationAck from the HLR.
 10. The communication nodes according to claim 9,further comprising: means for transmitting a Routing Area Update Acceptto the mobile communication device; means for receiving a Routing AreaUpdate Complete from the mobile communication device.
 11. Thecommunication nodes according to claim 8, further comprising: means fortransmitting a Routing Area Update Accept to the mobile communicationdevice; means for receiving a Routing Area Update Complete from themobile communication device.
 12. The communication nodes according toclaim 8, wherein the security functions use encryption.
 13. Thecommunication nodes according to claim 8, wherein the communication nodeand the other communication node are arranged within a mobilecommunication network.
 14. The communication nodes according to claim 8,wherein the mobile communication network uses GPRS or UMTS.